For a PCB which mates with an edge connector, it is often necessary to automatically short together a plurality of edge conductor pads on the PCB while the PCB is disconnected from the edge connector in order to protect the PCB's circuitry from ESD. Such ESD protection devices have been either custom designed for use in a specific PCB-edge connector or off-the-shelf for use in many different PCB-edge connector types.
A custom designed ESD protection device is typically fabricated on the PCB and coupled with a specifically configured edge connector which together provide the conductor pads with effective protection against ESD. An example of such a custom designed ESD protection device is illustrated in U.S. Pat. No. 4,179,178 issued to Bachman et al. on Dec. 18, 1979. This patent shows an edge connector having a pair of elongated ground pins for mating with complementary receptacles disposed in a cartridge which surrounds the PCB. Within the cartridge and disposed above the PCB resides an ESD protection device that includes a protuberant region which extends laterally over both the conductor pads and the receptacles. The protuberant region has a plurality of fingers arranged over the PCB so that each finger is disposed over a corresponding conductor pad. When the PCB is disconnected from the connector, each protuberant finger conductively engages the associated conductor pad. This shorts all the conductor pads together and protects them from ESD. Correspondingly, when the edge connector is mated with the PCB, the pair of ground pins displace the protuberant region from the receptacle so that the protuberant fingers disengage from the conductor pads.
Although providing effective ESD protection, this custom-designed device along with most custom-designed ESD devices suffer from a lack of interchangeability. That is, only the custom designed edge connector and no others can successfully mate with and operate with a PCB that employs such a custom designed device. This lack of interchangeability coupled with the large number of different custom-designed ESD protection devices has hindered widespread application of these devices within the PCB industry. Moreover, acceptance of these custom designed devices has been further hindered by (1) the high cost to manufacture these devices, (2) the added complexity that these devices introduce into the PCB manufacturing process, but most importantly, (3) the reduction in PCB chip density because of the board space that these devices occupy.
For all of the above reasons, PCB manufacturers presently employ a variety of off-the-shelf devices to protect their PCB circuitry against ESD. For example, the typical "add on" PCB for a personal computer presently arrives from the manufacturer with either conductive foam or wires disposed around the conductor pads, with the entire PCB sealed within an ESD protective bag, which is itself sealed within a box containing conductive foam pellets. These off-the-shelf devices (i.e., conductive foam and protective bags) provide the PCB with effective ESD protection until the User removes the wires or conductive foam from the conductor pads. At that point, the PCB is vulnerable to ESD because all the ESD protective devices have been removed. Accordingly, when the User subsequently attempts to place the PCB into an edge connector, a sizable number of the PCB's could be damaged by ESD and would have to be replaced. Consequently, a need still exists within the PCB industry for an off-the-shelf device which effectively protects the PCB from ESD until the PCB is mounted to an edge connector.